The aim of the paper is to investigate the effect of groundwater flow on Gaomiaozi bentonite(GMZ). The expansion-permeameter and turbidity meter are used to measure the turbidity of erosion liquid and the expansibility of bentonite samples. The influence of such factors as the dry density of bentonite, pH value and flow direction of erosion solution, type & concentration of solution, and crack amount of surrounding rocks is analyzed. It can be concluded that: the expansibility of bentonite increases dramatically during the first several days and remains stable then; the higher dry density of the bentonite, the weaker erosion presents on bentonite; pH value has a great influence on the erosion of bentonite, and the erosion is weaker under a higher alkaline conditions and vice versa; radial seepage of water flow has a greater effect on the erosion of bentonite than vertical seepage; and the erosion of bentonite becomes more intensive if the crack amount increases; the erosion of bentonite firstly increases and then decreases as NaCl concentration in erosion solution increases; the influence of CaCl2 concentration on bentonite is similar to that of NaCl, but the effect of CaCl2 is less significant.